Field of the Invention
The present invention relates to the manufacture of a metallic honeycomb body, in particular for exhaust gas catalytic converters for automotive vehicles, which is wound, layered or looped from at least partially structured sheet metal layers, and is brazed at least in some areas.
In order to catalytically convert exhaust gases in exhaust gas systems of motor vehicles with internal combustion engines, metallic honeycomb bodies are used which serve as a support for a catalytically active material. It is crucial for the durability of such catalytic converter supporting bodies and for the efficiency of similar honeycomb bodies in different areas of application, that the individual sheet metal layers from which the body is composed are connected together by high quality brazed joints, in at least some areas. It is known that such honeycomb bodies are composed from steel sheets resistant to high temperature corrosion, and are brazed in a high temperature vacuum.
Such honeycomb bodies are described, for example, in Published, Non-Prosecuted German Patent Applications DE 23 02 746 A1 and DE 29 24 592 A1. Methods for brazing the honeycomb bodies are also known from these applications.
Furthermore, a method for gluing and brazing metallic honeycomb bodies is known from European Patent EP 0 049 498 B2, which makes possible the application of reduced quantities of brazing material. Further, a method for gluing and brazing such supports is described in Published, Non-Prosecuted German Patent Application DE 38 18 512 A1. This application also includes an overview of known brazing methods. The known brazing methods also include the dry brazing of honeycomb bodies described in Published European Patent Application EP 0 136 514 A1, in which brazing powder is held by surface forces and mechanical adhesion to the layers of sheet metal.
Furthermore, a method for manufacturing a metallic honeycomb body is known from International Patent Application WO 93/25339, wherein at least the structured sheet metal layers of the honeycomb body are provided with a thin layer of a rolling oil, to the extent that this is not already present in the manufacturing process. The rolling oil is subsequently subjected to a thermal treatment wherein the highly volatile components of the rolling oil are removed. The remaining residues of the rolling oil are brought into contact with a highly diluted aqueous solution of a tenside, whereby a layer forms which, after removal of the water by drying, forms an optimum condition for the application of brazing powder.